Dual-Phase PET-CT to Differentiate [18F]Fluoromethylcholine Uptake in Reactive and Malignant Lymph Nodes in Patients with Prostate Cancer

Purpose To investigate whether time-trends of enhanced [ 18 F]Fluoromethylcholine ([ 18 F]FCH) in lymph nodes (LN) of prostate cancer (PCa) patients can help to discriminate reactive from malignant ones, and whether single time point standardized uptake value (SUV) measurements also suffice. Procedures 25 PCa patients with inguinal (presumed benign) and enlarged pelvic LN (presumed malignant) showing enhanced [ 18 F]FCH uptake at dual-phase PET-CT were analyzed. Associations between LN status (benign versus malignant) and SUV max and SUV meanA50 , determined at 2 min (early) and 30 min (late) post injection, were assessed. We considered two time-trends of [ 18 F]FCH uptake: type A (SUV early > SUV late) and type B (SUV late ≥ SUV early). Histopathology and/or follow-up were used to confirm the assumption that LN with type A pattern are benign, and LN with type B pattern malignant. Results Analysis of 54 nodes showed that LN status, time-trends, and ‘late’ (30 min p.i.) SUV max and SUV meanA50 parameters were strongly associated ( P <0.0001). SUV max relative difference was the best LN status predictor. All but one inguinal LN showed a decreasing [ 18 F]FCH uptake over time (pattern A), while 95% of the pelvic nodes presented a stable or increasing uptake (pattern B) type. Conclusions Time-trends of enhanced [ 18 F]FCH uptake can help to characterize lymph nodes in prostate cancer patients. Single time-point SUV measurements, 30 min p.i., may be a reasonable alternative for predicting benign versus malignant status of lymph nodes, but this remains to be validated in non-enlarged pelvic lymph nodes.